Smaller yachts of the size 30 to 50 feet use what is known as a self-contained air conditioning system to cool the interiors of the yachts. In the simplest description this unit comprises a compressor, tube in tube condensing coil that uses water as the cooling medium, an evaporator coil, and a fan, typical of any self-contained AC unit that uses a tube in tube condenser. All of these components are mounted on one base pan. Yachts recirculate the air inside the cabins and only use a closed system of cooling. Depending on the size of the yacht, several units might be used to meet the cooling needs of the boat's interior. These self-contained air conditioning systems were introduced to the boating public around 1960 and have remained fundamentally unchanged in design and concept since that time. Dometic's Marine Air and Cruise Air divisions were the original developers of the concept.
On larger yachts where there is more room in the interiors, it is typical to use a split system air conditioning system. With this system the compressor and condensing coil are mounted in the engine room and air handlers consisting of the evaporator coil and fan are remotely mounted. Lines of compressed Freon gas connect the two assemblies. In addition chilled water systems can also be used on the larger yachts, where chilled water is produced in the engine room and pumped to air handlers that use finned coils and fans with the water as the cooling medium.
There are multiple challenges faced for cooling smaller boats. The size of the unit is an issue as it is typically mounted under a bunk top or sofa (settee). As bunks and built-in seating are about 18 inches off the floor and cushions are typically 4 inches thick, the structure of the seat leaves about 12-13 inches in height within which to work. Typically, 16,000 BTU compressors are about 12 inches in height. Thus, the largest self-contained systems are typically limited to 16,000 BTU in capacity. In addition to the height constraints, the width of the units is also constrained by the usual curvature of the hull outboard of the seats or bunks, both fore and aft and vertically. Packaging and overall configuration are critical and dictated by the interior layouts of a typical yacht.
As mentioned, the air conditioning systems are closed loops, recirculating the cabin air. For the air to reach the self-contained unit, it must pass through a grill in the front of the interior cabinetry and then pass through the evaporating coil and blower to be forced down ducting to be discharged at the appropriate locations in the interior of the yacht to provide uniform cooling. The vertical compressor and large fan of the self-contained unit makes it noisy and contributes to vibration. Yachts are usually made of fiberglass and plywood which are easily set into motion as these materials are flat and have a low modulus of elasticity (flexible). In addition, sound comes out through the grills mounted in front of the unit directly into the living space. It is desirable to keep sound levels and vibration levels to the lowest possible limits.
There is a lot of expensive copper and copper nickel used in the construction of the air conditioning units. Any increase in thermal efficiency results in a more efficient unit, i.e., more BTU's produced, packaged in the same size envelope, or if the same output was desired the components could be downsized and hence the cost and size of the components. In addition, there is limited power available on the docks of the marinas. If increased efficiency was possible, less power would be consumed to produce the same cooling capacity. Both cost and power consumption are very important in the industry.
As can be seen in FIGS. 1-5, the current standard configuration of air conditioner 20 includes evaporator coil 22 having a rectangular shape. On the other side of coil 22 is centrifugal blower 24 with motor 26 mounted outside of fan wheel 28. Incoming air 30 travels through coil 22, enters close coupled fan 24 and exits forward or aft in the vessel (not shown). In most designs, housing 32 of blower 24 can be rotated around a horizontal axis as depicted by bi-directional arrow 34 so output 36 of fan 24 points in the desired direction (See the difference in the position of housing 32 and output 36 as depicted in FIGS. 3 and 4). It should be noted that the airflow over evaporator coils 22 (depicted as uni-directional arrows 38) is not uniform as can be readily seen in FIG. 5. Corners 40 of evaporator coils 22 experience little airflow in those regions as there is no provision made for air to flow in those areas. In short, the abrupt changes in direction of coupling 42 and non-aerodynamically arranged shapes thereof preclude reasonable air flow in those regions. In the scenario described above the ducting can only run fore and aft as the bunk top is directly above the unit, and since the total foot print of self-contained unit 20 is rectangular in nature, unit 20 has to be configured and mounted such that the long side is always parallel to the interior joinery.
Another configuration of an evaporator coil and fan was recently developed by Marvair, i.e., the Marvair Self-Contained Model 24. The coil is still the same rectangular coil as described above, but an inline blower is close mounted to the center of the coil and this fan discharges into a rectangular shroud that surrounds the fan and that is attached to the perimeter of the coil. This arrangement pressurizes the shroud which allows for holes in the shroud to be opened so that air can escape from the top or either side of the shroud. This eliminates the need to rotate a centrifugal blower discharge. This and the foregoing geometry utilize large rectangular coils through which flowing air must then enter into a small round inlet, e.g., coupling 42, to a blower, which is then abruptly diverted 90 degrees and exits through a hole not in line with the air flow exiting the fan. It is believed that this arrangement is very inefficient.
As can be derived from the variety of devices and methods directed to moving air through a set of evaporator coils and exiting a fan mounted in line with the coils, in particular a self-contained marine air conditioner incorporating these components, many means have been contemplated to accomplish the desired end, i.e., a cost effective, compact assembly that fits in the required space while permitting a variety of air flow directions. Heretofore, tradeoffs between cost, and performance were required. Thus, there is a long-felt need for a high efficiency self-contained marine air conditioning unit whose design can be used in split and chilled systems that are also used in the marine industry as well as other industries.